Manufacture of abrasive articles



June 2, 1942. R. c. BENNER ET At MANUFACTURE OF ABRASIVE ARTICLES Fild Jan. 22, 1941 a k i 4 4 Q o INVENTORS. RAYMOND c. BEN NER R'OMlE L. MELTON ATTORNEY.

Patented June 2, 1942 MANUFACTURE or annasrvnanrlctns 1- Raymond C. Benner and remit-L. Melton, Niagara Falls, N. Y., assignorsto The.

Carborundum Company, Niagara Falls, N. Y

a corporation of Delaware Application January-22, 1941, Serial Nb. 375,514

a 9 Claims. (C1.

This invention relates to "flexible abrasive webs and-to methods-of manufacturing said webs.

More particularly, it relates to abrasive materi-. als comprising a felted fibrous structure with abrasive grains incorporated internally of the web and/or-extending in partabove-the surface thereof. The invention also pertains tofibrous abrasive webs in which modifying agents, bindersand the like have been'incorporated toimpart T j 1 This application is a continuation-impart of our co-pending" application Serial No, 343,150,

desired properties thereto.

filed June 29; 1940.

So-called coated abrasive articles, such as 1 1 abrasive paper and cloth, discs and the like, are old and well known in the art,-but-thepresent invention should not be confusedfwi'th such*'articles since it differs therefrom by the absence of j the conventional backing. It represents an im- -provement' over such articles by reason of the elimination of. the backing and may be used for. --many purposes for which abrasive paper is adapted as well as inapplications forwhich the 1 .there isamaximum, amount of abrasive particles at oneflat surface of the web with the. amount of abrasive grainv progressively diminishing as the distance from that-"surface or the web becomes greaterytherejb'einglittle oi-no abrasive V Y graln'at the opposing or-.-back'j's urfa ce of the web. However, if desiredv thejgrain may be evenlyand- ;uniformlydistributed; flsft jamount or size throughout the web, or itrniayube applied in such a manner that the quantity oi -grain diminishes I equally from both surfaces of. the 'web toward the interior.v 'similarlytheremay-be created an abrasive-containing web in which there is a a graduation .of gritsize of abrasive grain through the, web from one surfaceto: the opposing surciently carry out polishing'or grinding operations. .A sizing or surface application of ad-- conventional abrasive paper is notsuited. In 1 addition, its fibrous, structure lends a strength and durability to the final'product not'to be expected in a baclrless product.

We have found that abrasive web materials can be readily and quickly producedby -collect- -ing loose fibers in-anydesired form, as for example, 'i'n acontinuous sheet, and incorporating abrasive material therein. The present inven.-- tionytherefore, provides a flexible fibrous; abrasive web material in which the abrasive grain is v distributed internally of aloo'se flimsy web of any suitable fibrous material. Furthermore, the abrading action not confined to a superimposed: layer of abrasive grains on the upper sur- 'face of the web but the abrasive properties extend substantially all-the way through said web, there being no distinct line of demarcation between the fibrous-web and the upper abradingsurfacewln other words, webs having an upper surface application of abrasive grainsas herein provided are so constructed that the abrasive grain andnadhesive binder'permeates-and penehesive may be applied to the layer of abrasive grains in order to anchor them more firmly m position. v

' Various modifying agents, such "as water-proofing compounds,anti-friction agents, embrittling materials, flexibilizers and. other fillers, may be incorporatedin .the. web during manufacture in order to render the web resistant towater or impart specific desirable properties to the web.

The amount and distribution of each specific modifying agent would depend 'uponthe desired "web properties and'thejparticular portions of the web to be aifected thereby. 1 r

' Inorder that theinvention may be more clear- I 1y set forth and made more understandable reference is madev to. the accompanying drawing, in

which:

Y liigure, 1 isa greatly enlarged vertical crosssection throughv afragment of anabrasive web 1 embodying the present invention;

hates the fibrous web within the interstices .be-, tween the individual fibers which then assist in holding the projecting abrasive grain firmly in position.

Abrasive grain can'be introduced entirely or partially-within the web structure in amount and character to suit the conditionsand 'nature of I the lntended usei For example, the abrasive grain may be applied in such a. manner that- 4-5 I Figure 2 is a similarly enlarged vertical crosssection ofa modified form ofv abrasive web;

Figure 3 is. still anothermodification of the 1 invention; and t a Figure 4 isle-diagrammatic side elevation, part- {0 ly "in section,-showi ng one form of apparatus for making abrasive webs according-to the pres- .ent invention.

. In Figure 4 we have illustrated one form of I apparatus which may be employed in manufacturing abrasive webs comprising a felted fibrous material with abrasive grains incorporated sist of any fibrous material capable of being carded into web form or separable into individual fibers. Suchmaterials include natural fibers, such as cotton, wool, jute, flax and asbestos, as

well as the various synthetic fibers, such as glass 7 W001, resinous and rubber-like fibrous substances. Any one of these fibrous materials may be used singly or two or more may be mixed in any desired proportion. Cotton fibers have been found to be highly satisfactory in the present process and consequently will be used as a specific example in connection with the detailed description of the apparatus and method of manufacture.

The carded membranes are discharged through orifices or slots 9 in the floor I!) and onto a continuously moving conveyor belt, I I which is slightly wider than the width of the deposited membranes. As the membranes pass through the slots 9 they areshielded from any undesirable external influences, such as strong air currents, by the surrouding sidewalls l2 and iii. The conveyor belt II is provided with a smooth outer surface and is supported at the opposite ends thereof by the rolls l4 and i5, which are driven by any suitable means (not shown). The speed of the belt issynchronized with the rate of feed of the membranes so as to prevent any appreciable strain or pull on the flimsy membranes during their deposition.

The individual laps 5, 6, 1 and 8 are applied successively to form a composite layer of proper thickness and character.- The number and arrangement of the carding assemblies will depend upon the desired thickness and type of fibrous web produced.

Abrasive grains may be incorporated internally of the fibrous web by any one of several methods, such as by applying the grain to the deposited membranes duringthe steps of building up the web on the conveyor belt. Suitable apparatus for carrying out this step of the operation is illustrated in Figure 4 of the drawing, in which the abrasive grain is fed in regulated amounts from the several 'grain hoppers I6, I! and I8, each of which is provided with an adjustable feed gate l9 and cooperating grain distributing roll 20. After one or more layers of fibrous membrane have been deposited on the carrier, the feed gate IQ of grainhopper I6 is adjusted to feed a very thin stream of abrasive grain 2| onto the fibrous membrane. The next membrane 6 is then applied over this layer of deposited grain and the next increment of abrasive grains Zia deposited from the hopper H, the amount of grain being somewhat in excess of the amount of grain previously applied from hopper Hi. In this way alternate layers of abrasive grain and membranes or laps are deposited upon the conveyor belt and each successive application of abrasive grain may be heavier in amount than the previous application. If however, a uniform distribution of grain through the web is desired, then the grain feed from the sevcase the smallest particles may be applied from the first bin I6 and the size of the abrasive particles gradually increased inihe successive bins I! and I8. While only four bins for abrasive grains and four carding machines have been shown, it is to be understood that any number of layers of abrasive grain and carded membranes may be incorporated to produce a composite web of any desired thickness and character.

In practicing our invention any of the abrasive materials in common use may be employed, such as silicon carbide, fused aluminum oxide, fiint, corundum, emery, rouge and similar substances. The size of the abrasive particles may vary from the finest polishing or buffing powders to the coarser grit sizes used in grinding.

It is desirable, in certain instances, to incorporate an adhesive binder between the successive layers of fibrous membrane. This adhesive may be in powdered or liquid form and may be I either a glue, resin, rubber or rubber-like material. Such adhesives may be applied in any suit- I able manner, such as for example, mixing with the abrasive grains and applying from the grain hoppers I 6, l1 and I8, or separate hoppers and feed rolls may be utilized. Alternatively, the abrasive grains may be individually coated with a suitable adhesive prior to deposition onto or inclusion within the fibrous web. The adhesive may also be applied as a liquid in finely atomized form from suitable spray nozzles, provided the atomizing pressureis kept sufficiently low to avoid disturbing the flimsy membranes.

The abrasive-containing fibrous web may be further modified by the application of various modifying agents during various stages of the building up ofthe web in the same way in which the adhesive is added and in any required amount. For example, the web can be waterproofed by the application of a waterproofing agent to the membranes as they lie on the carrier belt, or by the use of a waterproof adhesive binder. Again antifriction ingredients of soapstone, graphite, and the like, can be similarly incorporated in those laps or membranes making up the portion of the web immediately adjacent the back surface. At any stage in the building up of the web, fiexibilizing, embrittling, or other agents may be similarly incorporated.

After the fibrous abrasive web I, with or without adhesive binders and/or modifying agents, has been built up to the required thickness it is ready to be compacted to a greater density for added strength. At the same time it is usually desirable to incorporate a liquid adhesive within said web to .bond the compacted fibers and produce a dense web having a strength comparable to that of paper or cloth.

The web I is initially compacted by the synchronously driven squeeze rolls 22 and 23,.which may be located near the terminus of the supporting belt ll. One or both of these rolls may have a resilient surface or they may have a roughened surface possessing a multiplicity of small projecting points. In either case the individual fibers of each successive lap or membrane are pressed down and around the base of each individual abrasive particle, securely anchoring it in place, and causing the uppermost grains to project above the web surface to form 28 applies binder adhesive to permeate 2,284,716 an extremely sharp and fast cutting abrasive material.

Passing from the compacting rolls the web is fed onto a moving conveyor belt 24, which is supported by the synchronously driven rolls 25 and 26, and delivered to the adhesive binder applying rolls 28, 29. The liquid adhesive binder is containedina pan 30, which may be waterjacketed and heated as required. Revolving roll 23 is partially immersed in the adhesive and with After the abrasive web is compacted and the.

proper amount of adhesive binder applied therethrough, it is passed over a suction drum and idler roll 4| to a suitable chamber where it is dried or cured. This chamber contains an endless conveyor 42 which serves to festoon the web J onto supporting sticks 43 and to transport these sticks and looped material to the moving rack 44. The speed of thisz'moving rack 44 is so adjusted that the material is properly set or cured by the time it reaches the end of the chamber.

' When the abrasive material is taken down from the rack it may be cut up into sheets, discs or belts of suitable size or additional coatings may be applied as will be hereinafter described.

In a modified form of the present process, we

may apply an additional layer of abrasive grains to the outer surface of the web after the fibrous abrasive web has been built up and compacted.

In carrying out this additional step of the process; we apply a layer of 'adhesiveto the outer side of the fibrous abrasive web by conventional adhesive applying means, such as the glue pan 30, adhesive roll 29, and a pressure roll 23. A layer of abrasive grain of predetermined thickness may be applied to the adhesively coated surface of. the

web by any of the well known methods for applying abrasive grains, such as, for example, anarrangement similar to the grain hopper l8 and the grain distributingroll 20 shown in Figure 4. The conventional sizing layer of adhesive is applied over the deposited layer of abrasive grains by theusual adhesive rolls, similar to those used in spreading the base coatingof adhesive.

The surface coating of abrasive grain may be applied at any time before or after partial or complete drying and curing of the abrasive filled fibrous web.

The abrasive grain maybe applied to a preformed fibrous web by gravitational forces, as described above, or by the more recently developed electrostatic, magnetic or mechanical methods of grain deposition. In these. new grain deposition/units. electrical and/or mechanical forces are utilized to orient the elongated abrasive particles and project them onto the fibrous web so that they are positioned with their longer axis substantially perpendicular to the surface of the web. Fora more detailed description of suitable electrostatic, apparatus for orientation and projection of the abrasive granules onto an adhesively coated web, reference is made to Patent No. 2,187,624, issued January 14, 1940, to R. L. Melton, R. C. Benner and H. P. Kirchner. Suitable mechanical. apparatus for the orientation and deposition of abrasive grains is described in Patent No. 2,141,658, issued December 27, 1938;

and suitable magnetic orientation and projection apparatus is illustrated and described in Patent No. 2,254,531; issued September 9, 194i, t0 the same inventors.

In another modification of the present'process the abrasive grains may be applied to a previously formed lap or web. The formed lap may be moved past a single grain applying means, such as the hopper 39 and its cooperating grain feed roll l9, where the entire amount of grain may be deposited on and into the fibrous web at one application and then the hesive binder applied into the abrasive filled lap" y the rolls 28, 29.. Or,

ifdes'ired, and particularly with the finer abrasive materials (220 mesh in sizeand smaller) the grain may be uniformly mixed with the adhesive in the pan 30 and both the abrasive and the adhesive binder applied simultaneously to the already formed fibrous web. In either case the abrasive grain is lodged in the open spaces within the web and held in place by the surrounding fibers and adhesive. v

Figure 1 is a greatly enlarged vertical crosssection of a fragment of an abrasive fibrous web 'made according to' the present invention, in

which web the individual fibers 32 of the various membranes have been pressed around the bases of the individual grains 33, firmly anchoring ,them in place.- The abrasive granules 33' have been distributed throughout the web in such a way that thereis a maximum amount of abrasive grain'at'the topsurface 31 oftheweb with the amount of abrasive grain progressively diminishiug to'a minimum at the back surface 36.

Figure 2 shows a'web fragment similar; to that shown 1 in Figure 1. in which an anti-friction agent 34 has been incorporated in that portion of the web nearest the back surface 33. -.Anouter surface coating of abrasive grain 35 has also been applied to'the top side of the web.

Figure 3.is a modified web made according to the present invention wherein the abrasive grains incorporated in the web show a gradation of grit size from the large grit grain 3311 at the top surface'3l of the web down to. the small grit size 33b nearest the back 36 of the web.

Figures 1, 2 and 3' clearly'showhow the abrasive grains are 'held in place byxbeing intertwined by the long fibers whose lengthsiare several times-the dimension of, the individual abrasive grit diameters. Furthermorathe uppermost granules penetrate through and above the top layer of membrane fibers,. which'with the aid of an adhesive binder-anchors them in such position that the upper cutting edges are free for grinding and polishing operations.

We have found that the character of the abrasive material produced by the-herein-described process can be altered to any desired degree. by

variations in the quantity and character of the adhesive binder employed. By the addition of an embrittling agent or the use of a resinous adhesive which cures to'a brittle stage, We enable to produce an article in which the fibrous materials break away and expose new abrasive grains during subsequent abrading operations. Thus the multi-layer abrasive article acts in a manner similar to that of a grinding wheel. As the surface granules become dulled and are broken away, the impregnated and brittle fibers whichare exposed also break away and present a fresh layer of sharpabrasive'grains at the grinding surface. Obviously the rate of breakdown'of the fibrous membrane can be regulated and controlled to any desired degree by changes in-the character and quantity of the impregnating agent and the degree of penetration into the individual fibers. The degree of penetration of the individual fibers may be regulated by the use of various textile wetting out agents which are well known in the industry.

Very brittle characteristics may be imparted to the fibrous membrane by impregnating with a liquid phenolic resin such'as that commonly sold under the trade name Durite 8-2143. Suflicient resin should be incorporated in the fibrous web so that the resin comprises from 30% to 60% by weight of the impregnated fibrous material. The impregnated material may then be cured for approximately 2 hours at a temperature of 200 to 250 F. Ifincreased brittleness is desired, the length of the heat treatment may be extended and the curing temperature raised to 300 F.

A fibrous abrasive web possessing a lesser degree of brittleness may be produced by impregnating the fibers of the web with glue under conditions which will leave a dry glue residue of from 20% to 60% by weight of the impregnated fibrous membrane.

Flexibilizing agents may be incorporated in a portion of the web or distributed throughout, depending upon the type of product desired. Impregnation with a long oilsynthetic resin varnish, such as that made by Pratt and Lambert and designated by them as No. 1767, produces a strong and very flexible web. Suflicient varnish should be incorporated so that it will comprise 20% to 40% by weight of the impregnated fibrous web. The varnish may be cured by heating for approximately 2 hours at a temperature of 200 F.

In cases where a less flexible material is desired, we may use a material such as that sold under the trade name Bakelite varnish No. BV-6509 as the impregnant. Suflicient varnish should be incorporated in the web so as to leave a dry residue of 20% to 40% by weight, and the impregnated material cured from 2 to 4 hours at a temperature of 250 to 280 F.

Various plasticizers, such as glycerine, dibutylphthalate, and the like may be added to the varnish impregnating agents in order to increase their flexibility. The quantity of such material employed will depend upon the desired flexibility characteristics of the finished product and may, in some instances, amount to 40% of the combined weight of the varnish and plasticizer.

We have also found that abrasive articles can be produced in which the outer surface, containing the maximum quantity of abrasive grain, is of a brittle character and the opposite side is of a flexible character. Thus one surface of the article functions most efiiciently as an abrading device, while the opposite surface provides the necessary flexibility and strength to permit use as a grinding belt. disc and the like. Abrasive materials of such character may be produced by applying an embrittling impregnant to one side of the web and applying a flexibilizing impregnant to the opposite side.

The character of the abrasive web may be varied within \vide limits by regulating the relative quantity of embrittling and flexibilizing agents applied to the opposite sides of the web and the depth of penetration therein.

The present invention readily lends itself to the creation of abrasive articles of specific properties in definite controlled portions of the article without spreading such properties to other parts of the web where they are unnecessary or undesive binder, provides a strong supporting material and the abrasive grains included therein. are firmly anchored in position. The grains are held, in place by what may be called a double anchors age, achieved by engagement of the individual fibers entwined around the base of each individual grain and the adhesion of the binder a agent. I

Another important advantage is that an abrasive article made in accordance with the invention possesses a resiliency and flexibility which is impractical to obtain with abrasive coated paper or cloth. v

While we have specifically illustrated and described the preferred embodiment of our invention, it is to be understood that the invention may be otherwise embodied and practised within the scope of the following claims.

We -claim:

1. The process of manufacturing flexible abrasive webs which comprises feeding a plurality of thin carded fibrous membranes onto a moving endless support, applying abrasive grain to the deposited fibrous membranes, alternating I the deposition of additional fibrous membranes and abrasive grain until the web has been built up to the desired thickness, applying suitable adhesive binder and compacting the web.

2. The process of manufacturing flexible abrasive webs which comprises feeding a plurality of thin carded fibrous membranes onto a moving endless support, applying abrasive grain to the deposited fibrous membranes, alternating the deposition of additional fibrous membranes and abrasive grain until the web has been built up .to the desired thickness, incorporating a waterbuilt up to the desired thickness, applying suit? 1 able adhesive binder and compacting the web.- 1.

4. The process of manufacturingflexible'abra: sive Web material which comprises feeding a plu-e rality of thin carded fibrous membranes onto a Fa moving endless support, adding a flexibilizing agent to the deposited flexibilized fibrous membranes, alternating the deposition of additional fibrous membranes and abrasive grain until the web has been built up to the desired thickness, impregnating the fibers of the lastly deposited membranes constituting the upper portion of the fibrous web with an embrittling agent to render the fibers friable in use, applying suitable adhesive binder and compacting the web.

5. The process of manufacturing flexible abrasive web material which comprises'forming a fibrous base from a plurality of superimposed thin carded fibrous membranes, and introducing The fibrous membrane structure,

abrasive grain and adhesive binder internally or the flbrous'web structure.

6. The method of manufacturing flexible abrasive articles which comprises incorporating abra-r sive grain and a suitable adhesive binder inter nally of a preformed web oi uncompacted fibrous material and compacting said web the desired density.

'1. A process of making flexible abrasiveweb material which comprises forming a flbrous base from a plurality of superimposed thin carded fiabrasive web which comprises forming an abrasive-containing web according to the method oi claim 1, and applying a final coating of abrasive grains and adhesive binder to the outer surface of said fibrous web. l

9. A process of making flexible abrasive web material which comprises feeding a plurality of brous membranes, rendering those membranes a in use, introducing abrasive grain and a suitablethin carded flbrous membranes onto a moving endless support, applying abrasive grain to the deposited fibrous membranes, alternating the deposition of additional fibrous membranes and ,abrasive grain until the'web has been built up to the desired thickness, progressively increasing the amount oi. abrasive grain applied between successive membranes whereby the resulting flbrous web has an abrasive grain'content progressively greater from one surface or the web to adhesive binder internally of the web, and coma pacting the web to the'desired density.

8. The method of making a flexible fibrous the oppoflng web surface, applying a suitable adhesive binder and compacting the web.

RAYMOND C. BENNER. ROMIE L. MELTON. 

